Contact bounce is a common occurrence during the activation or deactivation of electrical contacts. These electrical contacts may include: push-button switches; toggle switches; electromechanical relays; or power connection devices. FIG. 1A shows a graph of a typical contact bounce in an electrical circuit. The graph represents a digital signal 10 that is switched from off (low) 12 to on (high) 18. When the electrical contact is activated 14, the signal goes through a contact bounce period 16 until it eventually stabilizes. FIG. 1B shows an alternative graph of a contact bounce where the electrical contact is switched from on (high) 22 to off (low) 28. As can be seen, a contact bounce period 26 occurs when the contact is de-activated 24 in a similar manner as shown in FIG. 1A.
For devices such as a lamp or electric motor, contact bounce is not usually a problem. The contact bounce periods 16 and 26 lasts a minute fraction of a second and will not affect the performance of the device. However, if the device being used is micro-processor, contact bounce can have a significant impact on performance since these devices perform operations in microseconds.
FIG. 2 shows a schematic of a prior art embodiment of a xe2x80x9chot-swapxe2x80x9d controller circuit 30. xe2x80x9cHot-swappingxe2x80x9d or xe2x80x9chot-pluggingxe2x80x9d refers to the insertion and removal of circuit boards into an active device, such as a computer motherboard, while the device is powered on. This circuit 30 is design to control inrush current so that an integrated circuit board can be safely inserted to and removed from a live backplane. In this embodiment, the controller circuit 30 represents the LT(copyright) 1640 Hotswap(trademark) Controller produced by Linear Technology. Various pin connections for the chip are indicated by name in FIG. 2. The circuit 30 combines the controller chip 32 with additional components to provide control signals 33 to the system voltage converters (not shown). The power for the circuit 30 is provided by a power supply bus that includes: a 48 V line 34; a 48 V Return line 36; and a Board Engage (or Ground) line 38.
When the power supply bus is connected, the circuit may be susceptible to the problems of contact bounce. The contact bounce that results can cause an excess transient current and could potentially affect operation of the circuit 30. However, the controller circuit 30 includes a circuit breaker (not shown) that is internal to the controller chip 32. If the circuit 30 were to experience an excessive transient current, it would be transmitted from the GATE pin on the controller chip 32 through the output line 41 to the MOSFET 40. The MOSFET 40 would direct the majority of the excess current to the 48 V Return line 36. Additionally, a trace current would be transmitted back to the SENSE gate of the controller chip 32 via the trace current line 42. Upon receipt of a trace current, the circuit breaker within the controller chip 32 will go to a xe2x80x9cLatch Offxe2x80x9d state which disable the circuit 30.
In an alternative embodiment, the invention relates to a connection module for a hot-swappable system power supply bus comprising: a module body; a power return pin extending from the module body, the power return pin having a first length; a power supply pin extending from the module body, the power supply pin having a second length; and a system ground pin extending from the module body, the system ground pin having a third length, wherein the third length is less than the first length and the second length such that the system ground pin makes a connection with the hot-swappable system subsequent to insertion of the power return pin and the power supply pin.
In an alternative embodiment, the invention relates to a connection module for a hot-swappable system power supply bus comprising: means for connecting a power return source to the hot-swappable system; means for connecting a power supply source to the hot-swappable system; and means for connecting a ground source to the hot-swappable system such that the ground source is connected after a contact bounce period of the power supply source and a contact bounce period of the power return source.
In an alternative embodiment, the invention relates to a method for connecting a power connection module to a hot-swappable system comprising: creating an over-voltage condition in the hot-swappable system by connecting a power supply pin and a power return pin to a power supply bus; allowing a contact bounce period to elapse during the over-voltage condition; and connecting a system ground pin to the power supply bus after the contact bounce period has elapsed.
The advantages of the invention include, at least, a power connection module that prevents excessive transient current, due to contact bounce, from being detected, by creating an over-voltage condition that allows the contact bounce to terminate before the system ground is connected.